The invention is related to crude oil demulsification and aromatic sulfonic acid demulsifier formulations.
Produced crude oils contain varying amounts of water and inorganic salts like chlorides, sulfates and carbonates of Group Group I and Group II elements. The presence of salts present difficulties during crude oil processing such as corrosion of the oil processing equipment. In order to mitigate the effects of corrosion resulting from the presence of salts, it is advantageous to reduce the salt concentration to the range of 3 to 5 ppm by weight of the crude oil. This concentration corresponds to approximately 2 pounds of inorganic salts per 1,000 barrels of crude oil. One method to remove salts from a crude oil is to solubilize the salts in water and remove the water from the crude oil. Generally the water present in crude oil is either phase separated water or emulsified water. Emulsified water is water that is dispersed in oil as a water-in-oil emulsion. Demulsification is the method of removing the dispersed water from the oil. Generally when crude oil is produced from subterranean environments, salts like chlorides, sulfates and carbonates of Group I and Group II elements are dissolved in the water phase. Water with dissolved salts is generally called brine. Demulsification results in removal of water and a reduction in salt concentration. The value of crude oil is enhanced by reducing the levels of salts and water in the crude oil.
Among the crude oil demulsification methods in use today, electrostatic demulsification, gravity separation, centrifugation and hydrocyclone-assisted separation are frequently used. Wash water is added until the crude oils water content is in the range of 4 to 15 vol. %, and a chemical demulsifier formulation is added so that the oil and the aqueous phases can be separated by separation methods known in the art. As used herein, a crude oil emulsion is a mixture of crude oil and a suspended aqueous phase, which may be in the form of droplets stabilized by naturally occurring surface-active compounds in the crude oil. Additionally, inorganic solids such as clay or silica can also contribute to emulsion stabilization.
In electrostatic separation, dispersed brine droplets coalesce in between electrodes located in the oil phase. The coalesced aqueous droplets then settle below the oleaginous crude oil phase. The separation can occur in a separator where effluent brine can be removed. Treated crude is removed from the upper part of the separator. Intermediate between the oil phase and the brine phase is a xe2x80x9cragxe2x80x9d layer comprising a stable emulsion and solids. The rag layer may remain in the demulsifier vessel or it may be removed therefrom for storage or further processing.
Effective demulsification requires addition of a chemical demulsifier additive to the wash water or to the crude prior to application of an electrostatic field or centrifugal force to the crude oil emulsion. Crude oils that contain high amounts of asphaltenes and naphthenic acids are generally called heavy crude oils and are difficult to demulsify. These crude oils require specifically tailored demulsifier additives for demulsification to be effective. Many demulsifier additives have phenolic groups in their chemical structure. In some cases, crude oil demulsifier additives that do not contain phenolic groups and are effective on crude oils containing asphaltenes and naphthenic acids are desired.
In one embodiment, the invention is a crude oil demulsifier formulation comprising:
about 10 wt. % to about 80 wt. % based on the weight of the chemical demulsifier formulation of an additive having the formula:
Rxe2x80x94Arxe2x80x94SO3H
where R is an alkyl group containing at least 16 carbons and at least one branch of an alkyl group, Ar is an aromatic group with at least two 6-ring aromatic groups and
about 90 wt. % to about 20 wt. % based on the weight of the chemical demulsifier formulation of a co-additive selected from the group consisting of dipropylene monobutyl ether, aromatic naphtha, isoparaffinic solvent, cycloparaffinic solvent, aromatic solvent, diethylene glycol monobutyl ether, benzyl alcohol, and mixtures thereof.
In another embodiment, the invention is a process to demulsify a crude oil emulsion comprising:
adding to a crude oil emulsion a chemical demulsifier formulation comprising:
about 10 wt. % to about 80 wt. % based on the weight of the chemical demulsifier formulation of an additive having the formula:
Rxe2x80x94Arxe2x80x94SO3H
where R is an alkyl group containing at least 16 carbons and at least one branch of an alkyl group, Ar is an aromatic group with at least two 6-ring aromatic groups and
about 90 wt. % to about 20 wt. % based on the weight of the chemical demulsifier formulation of a co-additive selected from the group consisting of dipropylene monobutyl ether, aromatic naphtha, isoparaffinic solvent, cycloparaffinic solvent, aromatic solvent, diethylene glycol monobutyl ether, benzyl alcohol, and mixtures thereof.
separating said emulsion into a plurality of layers, and optionally, recovering demulsified crude oil.
Applicants"" discoveries are based on the fact that adding a chemical demulsifier formulation can enhance brine droplet coalescence in crude oil. The chemical additive in the formulation is a branched aromatic sulfonic acid of a certain structure. Application of electrostatic fields, centrifugation or hydrocyclone treatment enhances the process of coalescence of dispersed brine droplets. For a chemical demulsifier additive which, itself, is an acid to be effective as a demulsifier of an acid containing crude oil is unexpected because acids are known to those skilled in the art to be emulsifiers.
The combination of the additive and co-additive provides a synergistic effect and enhances demulsification performance. The combination of the aromatic sulfonic acid additive and co-additive comprises the demulsifier formulation. Co-additives selected from the group consisting of dipropylene monobutyl ether, aromatic naphtha, isoparaffinic solvent, cycloparaffinic solvent, aromatic solvent, diethylene glycol monobutyl ether, benzyl alcohol, and mixtures thereof are examples where synergistic behavior can be obtained.
While the invention can be practiced with any crude oil containing brine, it is preferably practiced with heavy or waxy crude oils. Heavy or waxy crude oils have one or more of the following characteristics:
The crude oil has an API gravity ranging from about 5 to about 30.
The crude oil has a high naphthenic acid concentration; characterized by a high xe2x80x9cTANxe2x80x9d number (the TAN number represents the number of milliequivalents of potassium hydroxide required to neutralize 1 gram of crude oil).
The fraction of the crude oil soluble in n-heptane ranges from about 0.5 wt. % to about 15 wt. %.
The invention can also be practiced on crude oil distillates, synthetic oils for example, silicone oils and vegetable or animal derived oils.
Chemical demulsifier additive useful in the practice of the invention has the structure:
Rxe2x80x94Arxe2x80x94SO3H
Preferably, the chemical demulsifier additive has an alkyl group R that is at least 16 carbons. The alkyl group is preferably branched. A xe2x80x9cYxe2x80x9d branched alkyl group is more preferred. The xe2x80x9cYxe2x80x9d branch may have further branching. The aromatic group, Ar, has at least two 6-ring aromatic groups. Preferably the rings are fused. Cycloalkyl groups can be attached to the aromatic rings. The cycloalkyl rings have at least 6 carbons and can be fused or pendant to the aromatic rings. The SO3H group can be attached to any position on the aromatic rings. Preferably at least 1 SO3H group is present.
The chemical demulsifier additive is used in combination with a co-additive. Co-additives useful in the practice of this invention include diethylene glycol monobutyl ether, dipropylene glycol monobutyl ether, aromatic naphtha, isoparaffinic solvent, cycloparaffinic solvent, aromatic solvent, oxygenated solvents, such as diethylene monobutyl ether benzyl alcohol, and mixtures thereof. The preferred formulation comprises about 10 wt. % to about 80 wt. % chemical demulsifier additive and about 20 wt. % to about 90 wt. % diethylene glycol mono butyl ether. Particularly preferred is a formulation of about 50% chemical demulsifier additive and about 50% diethylene glycol mono butyl ether.
An effective amount of the chemical additive and co-additive mixture (demulsifier formulation) is combined with the crude oil emulsion. An effective amount of the demulsifier formulation is the amount necessary to displace the surface-active component from the brine droplets and render the brine droplets more amenable to coalescence. The effective amount ranges from about 5 ppm to about 10,000 ppm based on the weight of the crude oil, with about 20 ppm to about 40 ppm being preferred.
Adding water to the crude oil that already contains water is a process called wash water addition. Wash water addition is optional. The amount of added water required for effective demulsification could be in the range of 1 to 20 wt % based on the weight of crude oil.
In a preferred embodiment, a crude oil containing dispersed brine and a chemical demulsifier formulation are combined, wash water is added, the mixture mixed and then demulsified under electrostatic desalting or demulsification conditions. Electrostatic desalting or demulsification is known to those skilled in the art of crude oil processing. By way of example, the crude is desalted in a vessel having electrodes at potentials ranging from about 10,000 volts to about 40,000 volts, A.C. or D.C. Voltage gradients present in the vessel range from about 500 volts per inch to: about 5,000 volts per inch, preferably at a potential ranging from about 500 to about 1,000 volts per inch. Crude oil temperature ranges 220xc2x0 F. to about 300xc2x0 F., and residence times range from about 1 to about 120 minutes, preferably from about 1 to about 15 minutes.
Mixing of the crude oil containing chemical demulsifier formulation and wash water can be conventional (xe2x80x9cstaticxe2x80x9d) or opposed-flow, and can occur in the same vessel as electrostatic demulsifier.
In opposed-flow mixing, two or more counter-currents of crude oil containing demulsifier formulation impact and intermingle with wash water. Opposed propeller (or impeller) and opposed jet (or nozzle) configurations are non-limiting examples of opposed-flow mixing. In the opposed-propeller geometry, at least two counter-rotating propellers are immersed in the crude oil-brine mixture in order to form opposed streams within the mixture. The streams of the mixture impact and intermingle in the volume between the propellers. The propellers may be in close proximity in the same reservoir or vessel, in different regions of the same vessel, or in connected vessels or reservoirs with baffles or pipes providing conducting means for directing the streams to a region where opposed-flow mixing can occur. Parameters such as propeller spacing, propeller angular speed, and the nature of any conducting means may be determined by those skilled in the art of mixing from mixture properties such as viscosity and the desired mixing energy.
In the opposed jet geometry, the crude oil containing demulsifer formulation and wash water are separated into at least two streams. Conducting can be carried out, for example, using pipes to direct the streams into an opposed-flow configuration. Accordingly, the longitudinal axes (the axes in the direction of flow) and the outlets of the pipes are oriented so that the streams impact and intermix in a region between the outlets. Preferably, two opposed pipes are employed and the angle subtended by the longitudinal axes of the pipes is about 180xc2x0. The outlets may be in the form of nozzles or jets. As in the opposed propeller geometry, parameters such as the surface area of the conduits, the flow rate of the mixture in the conduits, the size and shape of any nozzle or jet employed, and the distance between the outlets may be determined by those skilled in the art of mixing from mixture properties such as mixture viscosity and the desired mixing energy.
Mixing energy rates (mixing power) ranges from about 0.1 hp per 1000 gallons of the mixture of crude oil emulsion and chemical demulsifier to about 3 hp per 1000 gallons, with about 0.2 hp per 1000 gallons to about 0.5 hp per 1000 gallons being the preferred range. The invention can be practiced when the mixture""s temperature ranges from about 20 to 150xc2x0 C. Preferably, mixture temperature ranges from about 80xc2x0 C. to about 130xc2x0 C. The amount of added wash water ranges from about 0.5 to about 8.0 vol. % water based on the total volume of the crude oil, preferably from about 0.5 to about 3.0 vol. %.